This proposal is for a grant to develop a system of dosimetry for photoradiation therapy with injected hemotoporphyrin-derivative and visible light, already in use for treatment ofa variety of solid tumors. Improved dosimetry is required to assure achievement of an adequate therapeutic ratio, and to allow intercomparison of results from different investigators, using different irradiation systems and trating different sites. The aims of this investigation are to develop data, instrumentation, and procedures for measurement or calculation of the distribution of the light energy flux density with depth, the concentration of hematoporphyrin-derivative, and other parameters requred to predict the dose hence photodynamic cytotoxic effect in photoradiation therapy. We propose to develop radiometers with special filters and suitable probes for measurement of the effective light power density in tissue and relationship to the source power, wavelength, and irradiation geometry. The concentration of hematoporphyrin-derivative will be measured in vivo and in biopsy specimens by fluorimetry, tested against other techniques. The effects of oxygenation and temperature will be studied. The dosimetry method will be tested for prediction of biological response in cell culture and in laboratory animals. The dosimetry instrumentation and procedures may then be used to design the protocol for photoradiation therapy of human tumors, including selection of irradiation source, optimum wavelength, irradiance and duration of irradiation, and optimum delay after injection of the hematoporphyrin-derivative at a given dosage.